Question

If the speed of a bike is increased by 6 km/h from its original speed it would have taken 2 hours less to cover 360 km. What is its original speed?
1. 36 km/h
2. 30 km/h
3. 72 km/h
4. 66 km/h

Answer 1

Correct Answer - Option 2 : 30 km/h

Given:

Speed of bike increased = 6km/h

Distance covered = 360 km

Time taken = 2 hours less than the previous time taken

Formula used:

Speed = Distance/Time

Calculation:

Let the original speed of the bike be x km/h

Original speed = Distance/Time = 360/T₁

⇒ T₁ = 360/x

And,

New speed of bike = Distance/Time = 360/T₂

⇒ T₂ = 360/(x + 6)

According to the question

(360/x) - [360/(x + 6)] = 2

⇒ (1/x) - [1/(x + 6)] = (1/180)

⇒ x(x + 6) = 180 × 6

⇒ x² + 6x - 1080 = 0

⇒ x² + 36x - 30x - 1080 = 0

⇒ (x + 36)(x - 30) = 0

⇒ x = 30 km/h

∴ The original speed of bike is 30 km/h.